Conventional window and door manufacture has commonly used wood and metal components in forming structural members. Residential windows are commonly manufactured from milled wood products that are assembled with glass to form double hung or casement units. Wood windows while structurally sound, useful and well adapted for use in many residential installations, can deteriorate under certain circumstances. Wood windows also require painting and other periodic maintenance. Wood windows also suffer from cost problems related to the availability of suitable wood for construction. Clear wood products are slowly becoming more scarce and are becoming more expensive as demand increases. Metal components are often combined with glass and formed into single unit sliding windows. Metal windows typically suffer from substantial energy loss during winter months.
Extruded thermoplastic materials have been used in window and door manufacture. Filled and unfilled thermoplastics have been extruded into useful seals, trim, weatherstripping, coatings, and other window construction components. Thermoplastic materials, such as polyvinyl chloride, have been combined with wood members in manufacturing PERMASHIELD.RTM. brand windows manufactured by Andersen Corporation for many years. The technology disclosed in Zanini, U.S. Pat. Nos. 2,926,729 and 3,432,883, have been utilized in the manufacturing of plastic coatings or envelopes on wooden or other structural members. Generally, the cladding or coating technology used in making PERMASHIELD.RTM. windows involves extruding a thin polyvinyl chloride coating or envelope surrounding a wooden structural member.
Polymer materials have combined with cellulosic fiber to make extruded materials. However, such materials have not successfully been used in the form of a structural member that is a direct replacement for wood. Common extruded thermoplastic composite materials cannot provide thermal and structural properties similar to wood or other structural materials. These extruded materials fail to have sufficient modulus, compressive strength, coefficient of thermal expansion that matches wood to produce a direct replacement material. Further, many prior art extruded composites must be milled after extrusion to a final useful shape. Typical commodity plastics have achieved a modulus no greater than about 500,000. One class of composite, a polyvinyl chloride/wood flour material, poses the added problem that wood dust, which can accumulate during manufacture, tends to be explosive at certain concentrations of wood flour in the air. Most commonly, polyvinyl chloride, polystyrene, and polyethylene thermoplastics have been used in such products.
Accordingly, a substantial need exists for a composite material that can be made of polymer and wood fiber with an optional, intentional recycle of a waste stream. A further need exists for a composite material that can be extruded into a shape that is a direct substitute for the equivalent milled shape in a wooden or metal structural member. This need requires a coefficient of thermal expansion that approximates wood, a material that can be extruded into reproducible stable dimensions, a high compressive strength, a low thermal transmission rate, an improved resistance to insect attack and rot while in use, and a hardness and rigidity that permits sawing, milling, and fastening retention comparable to wood members.
Further, companies manufacturing window and door products have become significantly sensitive to waste streams produced in the manufacture of such products. Substantial quantities of wood waste including wood trim pieces, sawdust, wood milling by-products, recycled thermoplastic including recycled polyvinyl chloride, have caused significant expense to window manufacturers. Commonly, these materials are either burned, for their heat value in electrical generation, or are shipped to qualified landfills for disposal. Such waste streams are contaminated with substantial proportions of hot melt and solvent-based adhesives, waste thermoplastic such as polyvinyl chloride, paint, preservatives, and other organic materials. A substantial need exists to find a productive, environmentally-compatible process for using such waste streams for useful structural members and, thus, to avoid returning the materials into the environment in an environmentally harmful way.